QFT, string temperature, and the string phase of de Sitter space-time - art. no. 125014

The density of mass levels rho(m) and the critical temperature for strings in de Sitter space-time are found. QFT and string theory in de Sitter space are compared. A "dual" transform is introduced which relates classical to quantum string lengths, and more generally, QFT and string domains. Interes tingly, the string temperature in de Sitter space turns out to be the dual transform of the QFT Hawking-Gibbons temperature. The back reaction problem for strings in de Sitter space is addressed self-consistently in the frame work of the "string analogue" model (or thermodynamical approach), which is well suited to combine QFT and string study. We find de Sitter space-time is a self-consistent solution of the semiclassical Einstein equations in th is framework. Two branches for the scalar curvature R(+/-) show up: a class ical, low curvature solution (-), and a quantum high curvature solution (+) , entirely sustained by the strings. There is a maximal value for the curva ture R-max due to the string back reaction. Interestingly, our dual relatio n manifests itself in the back reaction solutions: the (-) branch is a clas sical phase for the geometry with the intrinsic temperature given by the QF T Hawking-Gibbons temperature. The (+) is a stringy phase for the geometry with a temperature given by the intrinsic string de Sitter. temperature. 21 dimensions are considered, but conclusions hold generically in D dimensio ns. [S0556-2821(99)05120-6].